Polyester, as a synthetic fiber, exhibits remarkable versatility and has gained significant acceptance and utilization in the textile industry since its inception. It currently holds the prominent position as the dominant fiber in clothing production. However, polyester fiber faces certain limitations when it comes to dyeing, primarily due to the high glass transition temperature and absence of reactive groups. Earlier the carrier agents were employed during dyeing but it had detrimental environmental effects. Now a days, polyester fibers is being dyed using high-temperature and high-pressure processes with disperse dyes. To overcome these challenges, alternative dyeing methods for polyester fiber have been sought. One such technique is Mass Coloration or may be termed as Spin dyeing, where a color masterbatch is incorporated into the molten polymer during the melt-spinning process prior to fiber formation. This innovative approach eliminates the need of water resources and significantly enhances the environmental sustainability of the product. The present paper provides a comprehensive discussion on both Mass Coloration and Conventional Dyeing techniques, including their respective advantages and disadvantages. Additionally, technical and industrial aspects related to the coloration of polyester fiber via Mass coloration are thoroughly examined.